Over the recent years, wireless communication systems used for short to medium communication distances include the wireless LAN technique WiFi that is based on the 802.11 standard, the Bluetooth system that is based on the 802.15 standard, the Femto technique that is directed to indoor applications and derived from the mobile communication system, etc.
The 802.11-based WiFi technique is currently the most widely used wireless network transmission technology, mainly used in a wireless local area network (LAN) environment, which may be either an indoor or outdoor environment. The 802.11 system was evolved into 802.11a and 802.11g based on OFDM technology from the original 802.116 based on CDMA transmission mechanism. In the latest 802.11n version, the physical peak rate of 802.11n is up to 600 MBPS by bringing in many antennas. In MAC layer, the 802.11 system always adopts the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol based random Multiple Access. The protocol adopts the “competition” mechanism. A CAP and the terminal or STA obtain the right to use the open air interface. Once the competition success, air interface will be exclusive to the CAP of competitive success, in the transmission cycle. Due to adopt the competition mechanism, access networks don't need a central control node. The CAP and the STA hollow resources are equal in the competition of the air interface resource. The efficiency of the WiFi system is low, and the wireless resource waste is high. The basic cause of this problem is the fact that the CSMA/CA mechanism is a contention-based random multiple access mechanism, and the right to use radio resources is contended between access points (CAPs) and stations (STAs) or among different STAs through the CSMA/CA mechanism, whilst wireless channels are contended at the same time, in which case collision occurs and waste of radio resources ensues. In order to avoid such collision, the CSMA/CA mechanism requires the CAPs or STAs to randomly retreat while contending for wireless channels, but when all the CAPs and STAs retreat, although there are idle wireless channels, they are not being used, and this is also a great waste of the wireless channels. Due to reasons specified above, the 802.11 system is relatively low in efficiency. For instance, the physical layer of the 802.11g system can reach a peak rate up to 54 Mbps, but the rate achievable by the transmission control protocol (TCP) layer under a large data packet downloading service for is not more than 30 Mbps, and the peak rate achievable thereby is even lower under a small data packet service due to increase in the overhead ratio. In spite of the aforementioned deficiencies, the 802.11 system is flexible and independent of any centralized control mechanism, so relatively low equipment cost can be achieved thereby.
Evolved from the mobile communication system, the Femto technique that is based on the 3GPP standard is a novel technology directed to indoor coverage. Based on data statistics of the 3G system, approximately 70% of all data services occur indoors, so the indoor high-speed data accessing scheme becomes of great importance. The Femto base station, also referred to as a pico base station, is small and exquisite in volume (similar to the case of Wi-Fi) and flexible for deployment. Since it is evolved from the mobile communication system, the Femto base station inherits almost the entire characteristics of the mobile communication system. The Femto equipment merely combines its application scenario characteristics such as limited coverage range, fewer accessing users and so on, to lower the processing capability of the equipment, to thereby reduce equipment cost. Considering from the perspective of the duplexing mode, like the mobile communication system, Femto base stations can be classified into two types of duplexing mechanisms—frequency division duplexing (FDD) and time division duplexing (TDD). The uplink and downlink carrier resources of the FDD are symmetrical, but the service characteristic of asymmetry in uplink and downlink data flows of data services causes certain waste of resources to the FDD system for data services. The uplink and downlink of the TDD system operate on the same carrier, and are allocated with different radio resources by dividing time resources, so the TDD system is better adapted to asymmetrical data services required by uplink and downlink services in comparison with the FDD. However, it is difficult for the TDD duplexing mode of the mobile communication system (including the Femto system) and the static allocation of uplink and downlink resources to achieve dynamic adaptation of service requirements and resource divisions for various data services with different requirements, such as webpage browsing, mobile videos, mobile games and machine-to-machine (M2M), etc. As compared with Wi-Fi, since Femto makes use of a scheduling-based centralized control mechanism, there is no waste of radio resources caused by contention collision and random retreat between base stations or CAPs and terminals, or among the terminals, so the link efficiency is relatively high.
the Femto technology, its multiple access mechanism distributes orthogonal access resources for the different STA. it has fundamentally different with CSMA/CA random multiple access oriented to competition. Femto technology requires central control node to distribute orthogonal wireless resources for the STA. The different STAs complete transmission through time, frequency, code word even multiplexing air interface resources at the same time. In the physical layer technology, Femto technology based on the 3G system adopts CDMA transmission mechanism, Femto technology oriented to LTE and WiMAX system adopts OFDM transmission mechanism. Because of the OFDM technology is the mainstream technology of the future broadband wireless communication system, Femto technology are mentioned in the present invention refers to LTE and WiMAX Femto. Because of TDD technology can better adapt to the mobile Internet asymmetric business to relative FDD technology, therefore the Femto mentioned in the present invention refers to TDD Femto technology.
Although the Femto system is also scheduled to perform uplink and downlink communication and to allocate radio resources for different terminals, its statically configured frame structure cannot match flexibly allocated radio resources of the uplink and downlink, and cannot self-adapt to service changes with small granularity. Imbalance in the allocation of services and resources may result in long time queuing, reduction of user experience, or waste of channel capacity.
Face to the future broadband and narrowband data, considering the short distance wireless communication scenario, whether Wi-Fi system based on 802.11 technology, or the Femto technology evolve from the mobile communication systems have some disadvantages.
(1) Technical Defects of Wi-Fi
Although 802.11n technology achieves a peak rate at the physical layer up to 600 Mbps through a MIMO-OFDM technology, the random multiple access mechanism based on CSMA/CA used by the MAC layer degrades its TCP throughput greatly. CSMA/CA is a multiple access mechanism with competitions, and the conflict of competition is inevitable in the system. If there are two or more terminals, or the terminal competes with a CAP for the air interface at the same time, either party will fail due to the competition. This is the conflict of competition. Obviously, the conflict of competition is a waste of air interface resources. In the case of the conflict of competition, in order to avoid the further conflict of competition, all parties of the competition will initiate the random backoff. During the backoff process, there will be the situation where multiple competing nodes are waiting. At this time, although services are waiting for transmission, the air interface resources have not been rationally used, which will cause a great waste of the air interface resources. The conflict of competition and random backoff are the important factors causing the low efficiency of the 802.11 system. More importantly, with the increase in the number of terminals, the conflict probability index increases and the system performance becomes worse.
(2) Technical Defects of TDD LTE Femto
The uplink and downlink wireless resources of a TDD LTE Femto system are configured by the frame structure format statically, with the scheduling cycle of 1 ms being used as the minimum configuration unit. Facing abundant types of data services, its asymmetry in the uplink and downlink services is not consistent, and further this frame format configured statically is unable to self-adapt to the demands on various types of data services. When the service feature changes, the uplink and downlink resources initially configured are redundant or insufficient to a certain extent, which will not only cause the waste of the wireless resources, but also increase the service delay. Although scheduling is carried out for uplink and downlink communication and assignment of the wireless resources for different terminals, the frame structure statically configured is not helpful in assigning uplink and downlink wireless resources and self-adapting to the service change with a small granularity. In case of unbalance between services and resource configuration, a long time queuing will be caused, thus user experience is degraded, or the waste of channel capacity will be caused.